1. Field of the Invention
The present invention relates to a magnetic reproduction device provided with a plurality of magnetic heads having different azimuths, and more particuarly, to a magnetic reproducing device which automatically selects, in a reproducing operation, magnetic heads having an azimuth suitable to a type of recording.
2. Description of Related Art
Time lapse VTRs have been used for monitor and guard purposes, The time-lapse VTR, which is also called as a long-time VTR, can perform lone-time recording on one magnetic tape by frame-recording of image signals in contrast to VTRs for home use which make continuous recording of image signals on a magnetic tape,
A majority of time-lapse VTRs are based on VTRs for home use (e,g,, of VHS type, Beta type and 8 mm type) because necessary magnetic tapes are easily available and the VTRs can be manufactured with ease. The Lime-lapse VTRs of a 2-head helical scan type are classified into following types:
(1) Both of two magnetic heads have a (+) azimuth; PA1 (2) Both of two magnetic heads use a (-) azimuth; or PA1 (3) A magnetic head of a (+) azimuth and a head of a (-azimuth) are used.
The magnetic head of a (+) azimuth and the magnetic head of a (-) azimuth record signals onto magnetic tapes with different azimuths.
FIG. 1 schematically shows a head drum of a time-lapse VTR of a 2-head helical scan type in the prior art, and particularly, of the above type (1). In the figure, at 21 is indicated a rotary drum, to which two opposed magnetic brads A1 and B1 are attached with an angular space of 180 degrees between each other. These magnetic heads A1 and B1 carry out recording with the same (+) azimuth, and alternately record input signals onto a magnetic tape. Switching between the heads A1 and B1 is conducted in accordance with a head switching pulse provided from a drum servo circuit (not shown).
FIG. 2 conceptually shows tracks on a magnetic tape having signals recorded by the foregoing VTR. In the figure, at 31 is indicated a magnetic tape, including tracks A1 recorded by the magnetic head A1, and tracks B1 recorded by the magnetic head B1.
FIG. 3 schematically shows a head drum of a time-lapse VTR of the 2-head helical scan type, and particularly, of the above type (2). FIG. 4 conceptually shows tracks on the magnetic tape onto which signals are recorded by the VTR in
FIG. 3. Magnetic heads A0 and B0 are attached to a rotary drum 22. These magnetic heads A0 and B0 record with the same (-) azimuth, and alternately record supplied signals onto a magnetic tape 22. Other points of the structure are the same as those of the VTR of the above type (1), and thus will not be described in detail.
FIG. 5 schematically shows a head drum of a time-lapse VTR of the 2-head helical scan type, and particularly, of the above type (3). FIG. 6 conceptually shows tracks of a magnetic tape where signals are recorded by the VTR of FIG. 5. Magnetic heads A0 and B1 are attached to a rotary drum 23. The magnetic heads A0 and B1, which are of the (-) and (+) types, respectively, carry out recording with different azimuths, and record t,he supplied signals alternately onto a magnetic tape 33. Other points of the structure are the same as those of the VTR the above type (1), and thus will not be depicted in detail.
Signals recorded onto the tracks by the magnetic heads of a (+) azimuth of the time-lapse VTR cannot be reproduced with the magnetic heads of a (-) azimuth. Meanwhile, signals recorded onto the tracks with the magnetic heads of a (-) azimuth cannot be reproduced with the magnetic heads of a (+) azimuth. That is, tapes recorded with the time-lapse VTR of one type cannot be reproduced with the time-lapse VTR of another type. For example, tapes recorded with the VTR of the above type (1) cannot be reproduced with the VTR of the type (2). Conversely, tapes recorded with the VTR of the type (2) cannot be reproduced with the VTR of the type (1). Further, the VTR of the type (3) can reproduce tapes recorded by the VTRs of the types (1) and (2), with only one of the magnetic heads.
Since both recording and reproducing have been usually achieved in one time-lapse VTR, low compatibility of magnetic tapes causes no inconvenience. In recent years, however, time-lapse VTRs for monitor or guard purposes have come into wide use, and hence compatibility of tapes has become more important.
In order to comply with the above demand, a time-lapse VTR of a double azimuth 4-head type has been developed. FIG. 7 schematically shows a head drum and four heads of the double azimuth type. 20 represents a rotary drum, to which two opposed magnetic heads 1a and 1b are attached with an angular space of 180 degrees between each other. The magnetic head 1a is a (+) azimuth magnetic head, and the magnetic head 1b is a (-) azimuth magnetic head. There is also provided a (-) azimuth magnetic head 1c which is angurarly spaced by a predetermined angle .theta., e.g., 1.4 degrees from the magnetic head 1a with respect to the center of rotation of the drum 20. There is further provided a (+) azimuth magnetic head which is opposed to the magnetic head 1c in the diametrical direction of the drum 20.
For recording signals by the time-lapse VTR thus constructed, the (+) azimuth magnetic head 1a and azimuth magnetic head 1b are usually used, and the magnetic tape recorded in this manner will be reproduced with the magnetic heads 1a and 1b .
In the case where the magnetic tape onto which signals were recorded by the VTR of the above type (2), the tape is reproduced with the (+) azimuth magnetic head 1a and (+) azimuth magnetic head 1d. On the other hand, in the case where the magnetic tape with signals recorded by the VTR of the above type (2), reproduction therefrom is allowed with The (-) azimuth magnetic head 1b and (-) azimuth magnetic head 1c.
As described above, the time-lapse VTR provided with four heads of a double azimuth type can provide compatibility among magnetic tapes recorded by the VTRs of the above three types. However, if the type of time-lapse VTR recording the subject magnetic tape to be reproduced unknown, the tape is first reproduced with the ordinary (+) azimuth magnetic head 1a and the (-) azimuth magnetic head 1b , and then it is determined whether the reproduction correct or not from the reproduced pictures. If the reproduction is not correct, another combination of magnetic heads is manually selected by means of a switch, and this selecting operation should be repeated until correct pictures are obtained.